With speeding-up and high integration of circuit substrates, countermeasures for signal delay and generation of EMI have been demanded. An optical interconnection technique which has been attracting considerable attention addresses signal delay which is a problem caused by electric wiring, signal deterioration, and electromagnetic interference noise generated from the wiring, and enables high-speed transmission.
As a technique for high-speed signal transmission using light within a substrate, a technique referred to as an “optical interconnection” technique has been proposed (refer to Patent Document 1, for example). Patent Document 1 discloses a secondary optical waveguide layer, a semiconductor laser having oscillation modes switched from one to another, and an optical-path switching structure in which switches optical paths of light beams emitted from the semiconductor laser.
The optical-path switching structure is arranged such that a radiation angle is changed in the optical waveguide layer in accordance with a change of the oscillation mode of the semiconductor laser and emitted light is transmitted in the optical waveguide layer. Accordingly, a state of transmission of optical transmission signals in the secondary optical waveguide layer can be selected and degrees of freedom of arrangements of a light emitting element and a light receiving element are improved so that flexible reconfiguration of the light signal transmission is realized.
As a technique which applies such an optical interconnection technique to TFTs especially used for driving plain-surface displays, a technique which uses light for signal transmission to address signal delay caused by increase of sizes and large capacity display has been discussed.
On the other hand, a technique of transmitting a signal output from a solid-state image pickup element as light to a camera body unit which includes a detachable lens having the solid-state image pickup element has been proposed (refer to Patent Document 2, for example).    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2004-219882    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2006-196972